%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-5-6 on page II-183 in "Horizontal extensions in standard \LaTeX {}".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3examargin}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{171.0pt}

%StartShownPreambleCommands

%StopShownPreambleCommands

\begin{document}
\[ \widehat   {\psi_\delta(t) E_t h} \neq
   \widetilde {\psi_\Delta(t) E_t h}
\]
\[ \overline  {\psi_\delta(t) E_t h} \approx
   \underline {\psi_\Delta(t) E_t h}
\]
\[ \overrightarrow {\psi_\delta(t) E_t h} \cong
   \overleftarrow  {\psi_\Delta(t) E_t h}
\]
Combinations are possible too:
\[ \overline  {\overline {\psi_\delta(t) E_t h}}
   \leq
   \underline {\overrightarrow
                         {\psi_\Delta(t) E_t h}}
   \]
Braces have extra possibilities as explained below.
\[ \overbrace  {\psi_\delta(t) E_t h} \doteq
   \underbrace {\psi_\Delta(t) E_t h}
\]
\end{document}
